The widespread appearance of retinal lesions in patients with long-standing diabetes makes an understanding of the chemical basis of these lesions of major importance. Retinopathy is seen in 60-80 percent of long-term diabetics and is the commonest cause of newly diagnosed blindness in the age group from 30-65 years. The area of basement membrane composition and structure in the retinal vessels and lens capsule of the eye in diabetes has been a neglected one in view of the apparent association of these lesions with chemical alterations in the basement membrane of these tissues. The overall aim of this research project is to investigate the nature and structural basis for the basement membrane alterations in the human diabetic eye. The main questions to be answered are the following: 1. Are there differences in the amino acid and carbohydrate composition of retinal vessel and lens capsule basement membranes from normal and diabetic human eyes? 2. Are there qualitative and quantitative changes in the glycoprotein and collagenous components of eye basement membranes in diabetes? 3. Is the crosslinking of the basement membrane altered in retinal vessels and lens capsules from diabetic eyes? 4. Is there a correlation between the degree and nature of diabetic retinopathy, basement membrane thickening and the composition and structure of the basement membrane? The answers to these questions will be sought by the isolation, analysis and fractionation of basement membranes from human retinal vessels and lens capsules.